The present invention relates to a blade, of a gas turbine, having a wide turning angle and suitable to a heavy duty and high load gas turbine.
General blades of a gas turbine will be explained by referring to FIG. 7 to FIG. 12. A gas turbine generally comprises plural stages of stationary blades disposed annularly in a casing (blade ring or chamber), and plural stages of moving blades 1 disposed annularly in a rotor (hub or base). Two adjacent moving blades 1 are shown in FIG. 7.
The moving blade 1 is composed, as shown in FIG. 7, of a front edge 2, a rear edge 3, and a belly (or a belly side) 4 and a back (or a back side) 5 linking the front edge 2 and rear edge 3. Combustion gases G1, G2, as shown in FIG. 7, flow in a passage 6 between the belly 4 and back 5 of two adjacent moving blades 1 at an influent angle xcex11 (G1), and turn and flow out at an effluent angle xcex12 (G2). By the flow of combustion gases G1, G2, the rotor rotates in a direction of blank arrow U through the moving blades 1.
The width of the passage 6 (xe2x80x9cpassage widthxe2x80x9d) of the moving blades 1 in which the combustion gases G1, G2 flow gradually decreases from the front edge 2 to the rear edge 3 as indicated by solid line curve in FIG. 8. At the rear end 3, the width is minimum, that is, throat O. Thus, by narrowing the passage width between the moving blades 1, along the direction of flow of the combustion gases G1 and G2, the combustion gases G1 and G2 are expanded and accelerated, and the turbine efficiency is enhanced.
Recently, in the field of gas turbine, the mainstream is the gas turbine of high load with the pressure ratio of 20 or more and the turbine inlet gas temperature of 1400 degree centigrade or more.
As the gas turbine of high load, the following two types are known. One is a high load gas turbine in which there are a large number, for example, from four to five, of blades. The other is a high load gas turbine in which the work of each blade of each stage is increased without increasing the number of stages of blades, for example, remaining at four stages. Of these two high load gas turbines, the latter high load gas turbine is superior in the aspect of the cost performance.
To increase the work xcex94H of each blade in each stage, it is required to increase the blade turning angle xcex94xcex1 as shown in FIG. 9 and FIG. 10, and equations (1) and (2).
xe2x80x83xcex94H=Uxc3x97xcex94Vxcex8xe2x80x83xe2x80x83(1)
xcex94Vxcex8=Vxcex81+Vxcex82xe2x80x83xe2x80x83(2)
In equations (1) and (2), only the peripheral speed component Vxcex8 is defined in the absolute system, and the other peripheral speed components are defined in the relative system.
More specifically, symbol U denotes the peripheral speed of moving blade 1. The peripheral speed U of moving blade 1 is almost constant, being determined by the distance from the center of rotation of the rotor and the tip of the moving blade 1, and the rotating speed of the rotor and moving blade 1. Accordingly, to increase the work xcex94H of each blade in each stage, it is first required to increase the difference xcex94Vxcex8 between the peripheral speed components near the inlet of the combustion gas G1 and outlet of the combustion gas G2.
To increase the difference xcex94Vxcex8 between the peripheral speed components, it is required to increase the peripheral speed component Vxcex81 near the inlet of the combustion gas G1, and the peripheral speed component Vxcex82 near the outlet of the combustion gas G2.
When the peripheral speed component Vxcex81 near the inlet of the combustion gas G1 is increased, the influent angle xcex11 becomes larger. When the peripheral speed component Vxcex82 near the outlet of the combustion gas G2 is increased, the effluent angle xcex12 becomes larger. When the influent angle xcex11 and effluent angle xcex12 become larger, the turning angle xcex94xcex1 becomes larger (see FIG. 10). As a result, when the turning angle xcex94xcex1 is increased, the work xcex94H of each blade in each stage becomes larger.
Accordingly, as shown in FIG. 11 and FIG. 12, by setting the influent angle xcex13 and effluent angle xcex14 larger than the influent angle xcex11 and effluent angle xcex12 shown in FIG. 7, it may be considered to increase the turning angle xcex94xcex11 larger than the turning angle xcex94xcex1 shown in FIG. 10.
However, the following problems occurs when only the influent angle xcex13 and effluent angle xcex14 are set larger. That is, the passage width becomes the passage width as indicated by single dot chain line curve shown in FIG. 8.
As a result, as shown in FIG. 8, a maximum width 7 occurs at a position behind the front edge 2, and a minimum width 8 occurs at a position ahead of the rear edge 3, that is, a width smaller than throat O is formed. Therefore, as indicated by single dot chain line curve, a deceleration passage (diffuser passage) is formed from the front edge 2 to the maximum width 7, and from the minimum width 8 to the rear edge 3. Accordingly, the flow of the combustion gases G1, G2 is decelerated, and the turbine efficiency loss increases.
Thus, if only the blade turning angle is increased, the gas turbine with such blades is not suited to the heavy duty and high load. The problem is the same in the stationary blades as well as in the moving blades 1.
It is an object of the invention to present a blade, of a gas turbine, having a wide turning angle and suitable to a heavy duty and high load gas turbine.
The blade, according to the present invention, has such a shape that the diameters of circles inscribing the belly and back sides at different positions of adjacent blades decreases as one goes from the front edge to the rear edge. Since the blade has such a shape, even if the influent angle and effluent angle of gases are increased, a deceleration passage is not formed in the passage between the adjacent moving blades.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.